Parameters of the X-ray binary system Scorpius X-1

Abstract

ABSTRACT We modelled optical light curves of Sco X-1 obtained by the Kepler Space Telescope during the K2 mission. Modelling was performed for the case of strong heating of the optical star and accretion disc by X-rays. In the model considered, the optical star fully filled its Roche lobe. We investigated the inverse problem in wide ranges of values of model parameters and estimated the following parameters of Sco X-1: the mass ratio of components q = Mx/Mv = 3.6 (3.5–3.8), where Mx and Mv are the masses of the neutron and optical stars correspondingly; the orbital inclination was i = 30° (25–34°). In the brackets the uncertainties of parameters q and i are shown; these originated due to uncertainties of characteristics of the physical model of Sco X-1. The temperature of the non-heated optical star was T2 = 2500–3050 K, its radius was R2 = 1.25R⊙ = 8.7 × 1010 cm, and its bolometric luminosity was Lbol = (2.1–4.6) × 1032 erg s−1. The mass of the star was $M_v\simeq 0.4\, \mathrm{M}_{\odot }$. The contribution of the X-ray-heated accretion disc dominated in the total optical emission of Sco X-1. The transition between low and high states occurred due to the increase of X-ray luminosity by a factor of 2–3.